One document matched: draft-ietf-6man-addr-select-opt-04.xml
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<rfc category="std" ipr="pre5378Trust200902" docName="draft-ietf-6man-addr-select-opt-04.txt">
<front>
<title abbrev='DHCPv6 Address Selection Policy Opt'>
Distributing Address Selection Policy using DHCPv6
</title>
<author initials='A.M.' surname="Matsumoto" fullname='Arifumi Matsumoto'>
<organization abbrev='NTT'>NTT SI Lab</organization>
<address>
<postal>
<street>3-9-11 Midori-Cho</street>
<city>Musashino-shi</city>
<region>Tokyo</region>
<code>180-8585</code>
<country>Japan</country>
</postal>
<phone>+81 422 59 3334</phone>
<email>arifumi@nttv6.net</email>
</address>
</author>
<author initials='T.F.' surname="Fujisaki" fullname='Tomohiro Fujisaki'>
<organization abbrev='NTT'>NTT PF Lab</organization>
<address>
<postal>
<street>3-9-11 Midori-Cho</street>
<city>Musashino-shi</city>
<region>Tokyo</region>
<code>180-8585</code>
<country>Japan</country>
</postal>
<phone>+81 422 59 7351</phone>
<email>fujisaki@nttv6.net</email>
</address>
</author>
<author initials='J.K.' surname="Kato" fullname='Jun-ya Kato'>
<organization abbrev='NTT'>NTT SI Lab</organization>
<address>
<postal>
<street>3-9-11 Midori-Cho</street>
<city>Musashino-shi</city>
<region>Tokyo</region>
<code>180-8585</code>
<country>Japan</country>
</postal>
<phone>+81 422 59 2939</phone>
<email>kato@syce.net</email>
</address>
</author>
<author initials='T.C.' surname="Chown" fullname='Tim Chown'>
<organization abbrev='University of Southampton'>University of Southampton</organization>
<address>
<postal>
<street>Southampton, Hampshire SO17 1BJ</street>
<country>United Kingdom</country>
</postal>
<email>tjc@ecs.soton.ac.uk</email>
</address>
</author>
<date month="July" year="2012"/>
<!-- <area>Internet</area> -->
<workgroup>6man Working Group</workgroup>
<keyword>Internet-Draft</keyword>
<abstract>
<t>
RFC 3484 defines default address selection mechanisms for IPv6 that
allow nodes to select appropriate address when faced with multiple
source and/or destination addresses to choose between. The RFC 3484
allowed for the future definition of methods to administratively
configure the address selection policy information. This document
defines a new DHCPv6 option for such configuration, allowing a site
administrator to distribute address selection policy overriding the
default address selection parameters and policy table, and thus
control the address selection behavior of nodes in their site.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>
RFC 3484 <xref target="RFC3484"/> describes default algorithms
for selecting an address when a node has multiple destination and/or
source addresses to choose from by using an address selection policy.
In Section 2 of RFC 3484, it is suggested that the default policy table
may be administratively configured to suit the specific needs of a site.
This specification defines a new DHCPv6 option for such configuration.
</t>
<t>
Some problems have been identified with the default RFC 3484 address
selection policy <xref target="RFC5220"/>.
It is unlikely that any default policy will suit all scenarios, and thus
mechanisms to control the source address selection policy will be
necessary. Requirements for those mechanisms are described in <xref
target="RFC5221"/>, while solutions are discussed
in <xref target="I-D.ietf-6man-addr-select-sol"/> and
<xref target="I-D.ietf-6man-addr-select-considerations"/>. Those
documents have helped shape the improvements in
the default address selection algorithm <xref target="I-D.ietf-6man-rfc3484bis"/> as well as the DHCPv6
option defined in this specification.
</t>
<section title="Conventions Used in This Document">
<t>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described
in <xref target="RFC2119"/>.
</t>
</section>
<section title="Terminology">
<t>This document uses the terminology defined in <xref
target="RFC2460"/> and the DHCPv6 specification defined in
<xref target="RFC3315"/></t>
</section>
</section>
<section title="Address Selection options">
<t>The Address Selection option provides
the address selection policy table, and some other configuration
parameters.</t>
<t>
A address selection option contains zero or more policy table options.
Multiple policy table options in a Policy Table option
constitute a single policy table.
</t>
<t>The format of the Address Selection option is given below.</t>
<figure><artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_ADDRSEL | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |A|P| |
+-+-+-+-+-+-+-+-+ POLICY TABLE OPTIONS |
| (variable length) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Address Selection option format
</artwork></figure>
<t>
<list style='hanging' hangIndent='5'>
<t hangText="option-code:"> OPTION_ADDRSEL (TBD).
<vspace blankLines='1' />
</t>
<t hangText="option-len:">
The total length of the Reserved field, A, P flags,
and POLICY TABLE OPITONS in octets.
<vspace blankLines='1' />
</t>
<t hangText="Reserved:">
Reserved field. Server MUST set this value to zero and
client MUST ignore its content.
<vspace blankLines='1' />
</t>
<t hangText="A:">
Automatic Row Addition flag.
This flag toggles the Automatic Row Addition flag
at client hosts, which is described in the section 2.1
in RFC 3484 revision
<xref target="I-D.ietf-6man-rfc3484bis"></xref>.
If this flag is set to 1, it does not change client
host behavior, that is, a client MAY automatically
add additional site-specific rows to the policy table.
If set to 0, the Automatic Row Addition flag is disabled,
and a client MAY NOT automatically add rows to the
policy table.
<vspace blankLines='1' />
</t>
<t hangText="P:">
Privacy Preference flag.
This flag toggles the Privacy Preference flag
at client hosts, which is described in the section 5
in RFC 3484 revision
<xref target="I-D.ietf-6man-rfc3484bis"></xref>.
If this flag is set to 1, it does not change client
host behavior, that is, a client SHOULD prefer
temporary addresses.
If set to 0, the Privacy Preference flag is disabled,
and a client SHOULD prefer public addresses.
<vspace blankLines='1' />
</t>
<t hangText="POLICY TABLE OPTIONS:">
Zero or more Address Selection Policy Table options
described below.
<vspace blankLines='1' />
</t>
</list>
</t>
<figure><artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_ADDRSEL_TABLE | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| label | precedence | prefix-len | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
| prefix (variable length) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. Prefix Specific options .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Address Selection Policy Table option format
</artwork></figure>
<t>
<list style='hanging' hangIndent='5'>
<t hangText="option-code:"> OPTION_ADDRSEL_TABLE (TBD).
<vspace blankLines='1' />
</t>
<t hangText="option-len:">
The total length of the label field, precedence field,
prefix-len field, prefix field, and DASP options field
in octets.
<vspace blankLines='1' />
</t>
<t hangText="label:">
An 8-bit unsigned integer; this value is used to make a combination of
source address prefixes and destination address prefixes.
<vspace blankLines='1' />
</t>
<t hangText="precedence:">
An 8-bit unsigned integer; this value is used for sorting destination
addresses.
<vspace blankLines='1' />
</t>
<t hangText="prefix-len:">
An 8-bit unsigned integer; the number of leading bits in
the prefix that are valid. The value ranges from 0 to 128.
<vspace blankLines='1' />
</t>
<t hangText="prefix:">
A variable-length field containing an IP address or the
prefix of an IP address. An IPv4-mapped address <xref target="RFC4291"/>
must be used
to represent an IPv4 address as a prefix value.
The Prefix should be truncated on the byte boundary.
So the length of this field should be between 0 and 16 bytes.
<vspace blankLines='1' />
</t>
<t hangText="Prefix Specific options:">
Options specific to this particular Address Selection Policy option.
This includes, but not limited to, zero or one Zone Index option
that specify the zone index of the prefix in this option.
<vspace blankLines='1' />
</t>
</list>
</t>
<t>
The format of the Zone Index option is given below.
</t>
<figure><artwork>
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OPTION_ADDRSEL_ZONE | option-len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| zone-index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Zone Index option format
</artwork></figure>
<t>
<list style='hanging' hangIndent='5'>
<t hangText="option-code:"> OPTION_ADDRSEL_ZONE (TBD).
<vspace blankLines='1' />
</t>
<t hangText="option-len:"> 4.
<vspace blankLines='1' />
</t>
<t hangText="zone-index:">
The zone-index field is an 32-bit unsigned
integer, and used to specify the zone for scoped addresses.
The zone-index is defined in RFC 3493 <xref target="RFC3493"/> as 'scope ID'.
<vspace blankLines='1' />
</t>
</list></t>
</section>
<section title="Appearance of the Address Selection options">
<t>The Address Selection options MUST NOT appear in
any messages other than the following ones: Solicit, Advertise,
Request, Renew, Rebind, Reconfigure, Information-Request, and Reply.</t>
</section>
<section title="Processing the Policy Table option">
<t>
This section describes how to process received
Policy Table option at the DHCPv6 client.
</t>
<t>
This option's concept is to serve as a hint for
a node about how to behave in the network.
So, basically, it should be up to the node's administrator
how to deal with the received policy information in the way described below.
</t>
<section title="Handling of the local policy table">
<t>
RFC 3484 defines the default policy table.
Also, a user is usually able to configure the policy table
to satisfy his requirement.
</t>
<t>
The client implementation SHOULD provide the following choices
to the user:
</t>
<t>
<list style="hanging">
<t hangText="a)">
It receives distributed policy table, and replaces
the existing policy tables with that.
</t>
<t hangText="b)">
It preserves the default policy table, or manually
configured policy.
</t>
</list>
</t>
</section>
<section title="Handling of the stale policy table">
<t>
When the information from the DHCP server goes stale,
the policy received form the DHCP server should be
removed and the default policy should be restored.
</t>
<t>
The received information can be considered stale in
several cases, such as, when the interface goes down,
the DHCP server does not respond for a certain amount
of time, and the Information Refresh Time is expired.
</t>
</section>
<section title="Processing multiple received policies">
<t>
The policy table, and other parameters specified in this document
are node-global information by its nature.
So, the node cannot use multiple received policies at
the same time.
In other words, once the received policy from one source is
merged with another source, the policy is more or less changed.
The policy table is defined as a whole, so the slightest
addition/deletion from the policy table brings a change in
semantics of the policy.
</t>
<t>
It also should be noted that, when a node is
single-homed and has only one upstream line,
adopting a received policy table does not degrade the security
level.
</t>
<t>
Under the above assumptions, how to handle multiple
received policies is specified below.
</t>
<t>
A node MAY use Address Selection options in any of the following two
cases:
</t>
<t>
<list style="hanging">
<t hangText="1:">
The Address Selection option is delivered across the only secure,
trusted channel.
</t>
<t hangText="2:">
The Address Selection option delivery is not secured, but the node
is single-homed.
</t>
</list>
</t>
<t>
In other cases the node MUST NOT use Policy Table options
unless the node is specifically configured to do so.
</t>
<t>
<list style='hanging'>
<t hangText="Discussion:">
The secure trusted channel does not necessarily mean
a prioritized route in the routing table.
So, such a situation could happen that the traffic goes through a
non-secure, non-trusted channel and the host follows the
delivered policy from a secure, truested channel.
However, this policy is not for optimization of traffic and
resources at the local network and the hosts, but for
implementing the network policy to the hosts in the network.
</t>
</list>
</t>
</section>
</section>
<section title="Implementation Considerations">
<t>
<list style='symbols'>
<t>
The value 'label' is passed as an unsigned integer, but there is no
special meaning for the value, that is whether it is a large or small
number. It is used to select a preferred source address prefix
corresponding to a destination address prefix by matching the same
label value within the DHCP message. DHCPv6 clients need to convert this
label to a representation specified by each implementation (e.g.,
string).
<vspace blankLines='1' />
</t>
<t>
Currently, the label and precedence values are defined
as 8-bit unsigned integers. In almost all cases, this value will be
enough.
<vspace blankLines='1' />
</t>
<t>
The maximum number of address selection rules that may be conveyed
in one DHCPv6 message depends
on the prefix length of each rule and the maximum DHCPv6 message
size defined in RFC 3315. It is possible to carry over 3,000 rules
in one DHCPv6 message (maximum UDP message size).
However, it should not be expected that DHCP clients, servers and
relay agents can handle UDP fragmentation.
So, the number of the options and the total size of the options should
be taken care of.
<vspace blankLines='1' />
</t>
<t>
Since the number of selection rules could be large, an administrator
configuring the policy to be distributed should consider the resulting
DHCPv6 message size.
<vspace blankLines='1' />
</t>
</list></t>
</section>
<section title="Security Considerations">
<t>
A rogue DHCPv6 server could issue bogus address selection
policies to a client. This might lead to incorrect address selection
by the client, and the affected packets might be blocked at an
outgoing ISP because of ingress filtering. Alternatively, an IPv6
transition mechanism might be preferred over native IPv6, even if
it is available.
To guard against such attacks, a legitimate DHCPv6 server should
be communicated through a secure, trusted channel, such as a channel
protected by IPsec, SEND and DHCP authentication, as described in
section 21 of RFC 3315,
</t>
<t>
Another threat is about privacy concern.
As in the security consideration section of RFC 3484, at least
a part of, the address selection policy stored in a host
can be leaked by a packet from a remote host.
This issue will not be degraded regardless of the introduction
of this option, or regardless of whether the host is multihomed or not.
</t>
</section>
<section title="IANA Considerations">
<t>
IANA is requested to assign option codes to OPTION_ADDRSEL
, OPTION_ADDRSEL_TABLE, and OPTION_ADDRSEL_ZONE from the
option-code space as defined in section "DHCPv6 Options" of RFC 3315.
</t>
</section>
</middle>
<back>
<references title="Normative References">
&rfc2119;
&rfc3315;
&rfc3484;
&REVISE;
&STABLE;
</references>
<references title="Informative References">
&DTCONS;
&rfc2460;
&rfc3493;
&rfc4291;
&rfc4941;
&rfc5220;
&rfc5221;
&SELECTSOL;
</references>
<section title="Past Discussion">
<t>
<list style='symbols'>
<t>
The 'zone index' value is used to specify a particular zone for scoped
addresses. This can be used effectively to control address selection
in the site scope (e.g., to tell a node to use a specified source
address corresponding to a site-scoped multicast address). However, in
some cases such as a link-local scope address, the value specifying
one zone is only meaningful locally within that node. There might be
some cases where the administrator knows which clients are on the
network and wants specific interfaces to be used though. However,
in general case, it is hard to use this value.
<vspace blankLines='1' />
</t>
<t>
Since we got a comment that some implementations use 32-bit integers
for zone index value, we extended the bit length of the 'zone index'
field. However, as described above, there might be few
cases to specify 'zone index' in policy distribution, we defined
this field as optional, controlled by a flag.
<vspace blankLines='1' />
</t>
<t>
There may be some demands to control the use of special address types
such as the temporary addresses described in RFC4941 <xref
target="RFC4941"/>, address assigned by DHCPv6 and so on. (e.g.,
informing not to use a temporary address when it communicate within
the an organization's network). It is possible to indicate
the type of addresses using reserved field value.
<vspace blankLines='1' />
</t>
</list></t>
</section>
</back>
</rfc>
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